GCN Circular 14593
D. A. Kann, B. Stecklum, and F. Ludwig (TLS Tautenburg) report: We observed the optical afterglow (Cannizzo et al., GCN 14563) of the extremely luminous GRB 130505A (Cannizzo et al., GCN 14563; Golenetskii et al., GCN 14575) with the 1.34m Schmidt telescope of the Thueringer Landessternwarte Tautenburg equipped with a 4k CCD camera under good weather conditions. We obtained 3 x 300 sec frames in the Rc band. The afterglow is detected in each frame. For a nearby SDSS star (RA = 137.082047, Dec. = 17.486120), using the transformations of Lupton (2005), we find: B = 18.118, V = 17.080, Rc = 16.501, Ic = 15.967. Using this star for calibration, we derive a preliminary magnitude of Rc = 19.09 +/- 0.06 at 0.49118 days after the GRB. This message may be cited.